Are chronotypes (evening vs morning preference) and social jet lag (sleep midpoint
difference on weekends vs weekdays) associated with adiposity and cardiometabolic
risk in young adolescents? This cross-sectional study found that evening chronotypes
and greater social jet lag were associated with greater adiposity in adolescent girls,
but not boys, independent of sleep duration. There were no associations with a cardiometabolic
risk score. This study suggests that female adolescents may be more vulnerable to
the obesogenic effects of circadian misalignment; obesity prevention efforts should
consider regular sleep-wake patterns in addition to sleep extension and sleep quality
improvement. Inadequate sleep duration and quality increase the risk of obesity. Sleep
timing, while less studied, is important in adolescents because increasing evening
preferences (chronotypes), early school start times, and irregular sleep schedules
may cause circadian misalignment. To investigate associations of chronotype and social
jet lag with adiposity and cardiometabolic risk in young adolescents. Starting in
1999, Project Viva recruited pregnant women from eastern Massachusetts. Mother-child
in-person visits occurred throughout childhood. From January 23, 2012, to October
16, 2016, 804 adolescents aged 12 to 17 years completed 5 days or more of wrist actigraphy,
questionnaires, and anthropometric measurements. A cross-sectional analysis using
these data was conducted from April 31, 2018, to May 1, 2019. Chronotype, measured
via a continuous scale with higher scores indicating greater evening preferences,
and social jet lag, measured as the continuous difference in actigraphy sleep midpoint
in hours from midnight on weekends vs weekdays, with higher values representing more
delayed sleep timing on weekends. Adiposity, measured via anthropometry and dual-energy
x-ray absorptiometry. For a subset of 479 adolescents with blood samples, cardiometabolic
risk scores were computed as the mean of 5 sex- and cohort-specific z scores for
waist circumference, systolic blood pressure, inversely scaled high-density lipoprotein
cholesterol, and log-transformed triglycerides and homeostatic model of insulin resistance.
Among the 804 adolescents in the study, 418 were girls and 386 were boys, with a mean
(SD) age of 13.2 (0.9) years. In multivariable models adjusted for age, puberty, season,
and sociodemographics, associations of chronotype and social jet lag with adiposity
varied by sex. For girls, greater evening preference was associated with a 0.58-cm
(95% CI, 0.12-1.03 cm; P = .04 for interaction) higher waist circumference and 0.16
kg/m 2 (95% CI, 0.01-0.31 kg/m 2 ; P = .03 for interaction) higher fat mass index
as measured by dual-energy x-ray absorptiometry; each hour of social jet lag was associated
with a 1.19-cm (95% CI, 0.04-2.35 cm; P = .21 for interaction) higher waist circumference
and 0.45 kg/m 2 (95% CI, 0.09-0.82 kg/m 2 ; P = .01 for interaction) higher fat
mass index as measured by dual-energy x-ray absorptiometry. Associations of social
jet lag and evening chronotypes persisted for many measures of adiposity after adjustment
for sleep duration and other lifestyle behaviors. By contrast, no associations were
observed in boys. There were no associations with the cardiometabolic risk score for
either sex, although statistical power was low for this outcome. Evening chronotypes
and social jet lag were associated with greater adiposity in adolescent girls but
not adolescent boys. Interventions aimed at improving sleep schedules may be useful
for obesity prevention, especially in girls. This cross-sectional analysis of the
Project Viva cohort investigates associations of chronotype and social jet lag with
adiposity and cardiometabolic risk in young adolescents.